Parking outside a car can pick up leaves and pine needles. They can get caught up in the area by the windshield vent as well as the headlight buckets. Dirt and old leaves make a place to hold moisture for a longer time and that can make rust over the years. I think today most 914s that are restored will never see the type of use that the cars got back in the day as daily drivers. I thought nothing of parking my 74 out under a tree back in 78.
Moisture in the front hood seal made problems in the area by the headlight buckets as well.
Bob B